


The price of your mistakes

by Kaorukeehl



Series: Skeletons in the dark. [6]
Category: Undertale (Video Game)
Genre: Blood, Crime, Death, Graphic, Mass Death, Murder, Revenge, Revenge killing, Sneaking Around, Suspense, Violence, past loss
Language: English
Status: Completed
Published: 2020-04-22
Updated: 2020-04-22
Packaged: 2021-03-01 17:27:01
Rating: Explicit
Warnings: Graphic Depictions Of Violence, Major Character Death
Chapters: 1
Words: 5,374
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23790790
Author URL: https://archiveofourown.org/users/Kaorukeehl/pseuds/Kaorukeehl
Summary: Undertale Sans decides to finish some unfinished business from the past. Now he is on the hunt for blood. He knows that no one would believe that it was him who was behind all of this anyways. So the murders would end up as unsolved. Will Sans get away with what he is doing? Will anyone stop him before he claims more victims? How will this end?
Series: Skeletons in the dark. [6]
Series URL: https://archiveofourown.org/series/1532279
Kudos: 2





	The price of your mistakes

**Author's Note:**

> I made this on my phone. Hopefully I caught any autocorrects. 
> 
> Enjoy!

Undertale Sans walks along a city street. He turns to give a glance to a group. 

The group is attempting to rob a jewelry store. They have ski masks on, large hoodies, and baggy pants. They are wielding knives at the cashier. 

The cashier gives the robbers access to the jewels and the money. 

The robbers grab what they can and flee.

Spears shoot up blocking their path. 

They skid to a stop and turn to go another way. They find themselves surrounded by cops and Undertale Undyne. They drop everything raising their hands.

A successful swift take down of criminals.

'What idiots.' Sans can't help but think to himself as they robbers are put in handcuffs. 'They were sloppy and they didn't even bother to check who was around.' He turns away heading off on his way. 'I swear there are just too many idiots in this world.' He pauses in his walking to glance up at the sky. 

The sky is bright clear and blue. 

"I wonder if I'd be smart enough to make something unsolved." Sans whispers to himself with a slightly thoughtful hum. "You know I probably could. It'd be too easy too. I want to do it. I want to create unsolved murder." He lowers his head and decides to skip getting ketchup. He gets home to start figuring out a plan. He knows that he's going to have to make sure things work out the way he wants. He finishes and heads out with his plan. He looks around himself as he walks. He observes each and every person and monster he walks by. He needs to find the perfect being for his first crime. He has decided to go with someone who doesn't know him well. He doesn't want to immediately tie himself to a connection with the victim. He spots one monster he deems perfect for this. 

The monster is a dalmation dog though his spots are different colours. He has black spots on his right ear looking like a constellation. He has a large red spot his left ear. He has a blue spot on his jaw and cheek. He has a purple spot surrounding his left eye. The rest of his body is spotted with colours from the rainbow. 

Sans had seen this monster around a few times but hadn't gotten to know him. He begins following the dalmation monster planning how to kill him. He pretends to be interested in a few items to secretly spy on the other. 

The dalmation monster heads down an alleyway.

Sans goes after the other. He waits for him to be far enough away from prying eyes. He then leaps at the other monster.

The monster calls out in shock getting knocked to the ground.

Sans is quick to slam a bone into his targets neck. He knows to aim for a spot to quickly kill the other. He also uses it in order to keep the scream to a minimum. 

The monsters scream does become gargled, just as Sans wanted, and his body turns to dust.

Sans moves away making sure to still have his bone attack. He contemplates for a brief moment about leaving a message. He can't use anything too complicated. He knows that it would narrow down the suspect list; more than he would want it to be. He can't take the risk of making it complicated. Even if he knows no one will believe it's him. He also is aware he'll have to hide any LV he gains. He'll worry about that later. He really should focus. He turns swearing he hears someone heading this way. "No time." He whispers to himself and teleports away. 

A scream rings out when the one that was coming finds the dust.

Later that night Sans and Papyrus settle into the couch. They have their supper spaghetti and have decided to watch tv while eating. 

Papyrus turns on the tv which is currently on the news. He is about to change the channel when something catches his attention. 

"Breaking news! A monsters dust was found in an alley way today." The reporter tells them. "Police right now have no leads. They are working on trying to figure out who it is. And what happened."

"Hm. I wonder if that monster was involved in something they shouldn't have been." Sans guesses in lies. He just can't let Papyrus catch on. He can't let anyone catch on to what he's doing. He can't risk it if it's going to go unsolved. 

"If that is true then you had better not get into anything like that. I don't want whoever did this to target you." Papyrus turns to Sans.

Sans turns to look to his brother. He gives him one of his soft smiles. "Don't worry Paps. I don't get involved in such things." He tells him. "How about we switch the channel and get our minds off this? All we can do is speculate what happened after all." 

"Yes. I suppose you're right brother." Papyrus agrees and the two turn back to the tv. He changes the channel finding the movie about Undertale Mettatons rise to fame. "How about this?"

"Sure. That works." Sans agrees to that idea.

So Papyrus puts the remote down. He begins eating his food like Sans. 

The two enjoy the movie and Papyrus gets Sans to help in washing the dishes. They head to bed as it's getting a little late.

Sans is laying in bed staring up at the ceiling. He begins thinking about the past. He was a teenager and curiously wanted to watch his father work. He saw Gaster working on some machine.

Gaster had some of his followers with him. He had them become his main assistants. He did so as he wanted those who would be of better use. He didn't want to have to keep fighting for dominance. He had felt it wasn't worth the time. He had science to do. 

Sans looked up to him. He loved creating things. He was smart and had made smaller inventions using his intellect. He wanted to continue with this. He planned to become a scientist as well. He would make sure that no matter what he would be a scientist. He wasn't supposed to be there that day. 

Gaster didn't want him to come. He told Sans that he what something very important to do.

So Sans decided to sneakily watch it all. He kept most of his body hidden as he peered around the corner. 

Gaster moved away from the machine. "There. This baby is almost ready." He told his followers.

Sans had not seen this machine before. So he wondered to himself what it was supposed to do. 

"It's magnificent." One of the followers mentioned sounding happy. 

Sans ducked out of sight as some other monsters came into the room. 

"Is it ready?" One of the new monsters could be heard asking. 

"Not quite yet." Gaster informed the new comers.

"Looks ready to me." One monster responded and moved forward.

"No!" Gaster called out which caused Sans to look at what was going on once more. 

One of the new monsters were heading toward a switch.

Gaster tried to rush to stop this monster however he was held back by two others. "Don't do that! You don't know what you're doing!"

The monster grabbed the switch and turned to Gaster. "Actually. I think I do know what I'm doing." He flipped the switch turning on the machine.

A loud noise started and the machine rocked violently which caused all to look at it in fear. Jolts of electrocution ran up and down the body as the noise only got louder. 

The two monsters released Gaster who rushed over trying to turn it off... Sadly the switch was stuck and wouldn't move.

The new comer monsters bolted as a glow started to appear. 

Sans remembered their faces. He watched as suddenly Gaster was sucked into some kind of white portal. "NO!!!!" He screamed then ducked back into hiding when the others there got sucked in. He fell into the fetal position his skull held with his hands. He stayed sitting there his back was to the wall. He shut his eyes tightly only slightly opening them when a bright flash of light happened. He peeked back to check things as it was now quiet. He saw a very broken machine with no one in sight. 

Things only changed after that.

It seemed everyone except Sans had lost their memories of Gaster. So they won't understand what it is he is doing. 

Present day Sans glares at the ceiling. He believes that he remembers because he was there. He watched Gaster get sucked away never to be seen again. He also believes that it is his duty to avenge Gaster. He wonders if Gaster let him remember with the hopes that revenge could be dealt. He's just glad that Papyrus doesn't have to share the same burden of remembering. He smiles as he realizes that he could use this opportunity. He wants to make an unsolved case.

Why not finish some business from the past as well? 

Sans chuckles softly feeling like a mad genius. He shakes his head, to bring himself back to the moment, and closes his eyes to sleep. He has quite a bit to do. He gets up the next morning having breakfast pancakes with his brother. He waits until Papyrus heads out first then teleports. He lands at a building. He can remember hearing about this company the day before the incident. He wants to make sure his targets are indeed in there. He lifts goes to the side of the building in an alley. He lifts himself with blue magic hoping to not be noticed. He floats by the windows glancing in each room as he goes by. He tries to mimic the movements of a window washer moving upwards to clean. He pauses at about the tenth floor. He notices the group he needs. "Got ya." He smirks. He focuses on a spot hidden behind a plush chair. He teleports himself there so he can listen to their conversation. 

"Perhaps we could ask our Alphys to prepare it for us. I mean she is pretty smart."

"And a scientist. That's something we can't forget. We need a scientist if we want to push ourselves onward."

Sans eyes narrow. There is no way in hell hes going to let them cause the same thing twice. He has to take them down! He just needs to find when they are most vulnerable. He has to do it before something happens. 

"I think we'll need to discuss this a bit more. We've been holding off for so long because we wanted to be sure about things. So let's talk about it in the next few days to finalize everything. I'm going home."

"You still live on Anthony drive there?" Another asks so Sans takes a peek. 

The one monster, who is turned as if starting to leave but looked back to the others, is the one Sans focuses on. He is a griffin monster. He stands on two legs with the griffin looking body. He can use his front paws like hands. "Sure do." He confirms with a smile in the others direction. "Right by that crystal shop." He gives goodbyes not knowing they'd be his last ones. He carries a bag instead of slinging it over a shoulder. He heads to his car which Sans memorizes. He teleports to the store he's passed by a few times. He waits for the other to arrive. He doesn't want to tip off the monster. He's glad that they're monsters since it helps with the body.

No real body means no way to be sure how they died. Especially if it's just a pile of dust. 

Sans feels like the mixture, of getting revenge and creating unsolved murder, is the most fun he's had in a long while. He finds that it doesn't take long for the other to drive by. He teleports watching to secretly keep tabs on the car. He notices it pull up into an empty driveway.

No visible garage.

Good.

Sans watches from the corner of his eye as the other gets out. He turns his head as the door is unlocked. He tries to see what he can of the inside.

The door ends up being shut.

With a disgruntled mumble Sans heads over. He walks by the window peeking in. He feels like it's his lucky day as the curtains are open. He finds a spot to teleport to and goes there. He stays hidden behind the large grey couch. He hears the other move around for a few moments only to sit on the couch. He wouldn't be surprised if it was to watch tv. He moves to peek up managing to be able to do so. He doesn't see a phone in his hand. 

This is the perfect moment.

Sans uses the back of the couch to climb up. He moves swiftly to summon a kind of small pointed bone. He points the tip at the others throat. He gives the other a brief moment to react. He feels a need deep within in him to know of the fear and panic he's causing. 

"What the hell!?!" The monster starts to struggle, only to be weighed down by blue magic. "Why are you doing this!?!"

"For someone you'll never remember the name of." Sans keeps his voice low. He makes sure only the victim will hear him. He then proceeds to stab the others throat. 

Garbled noises can be heard at first before the victim slumps. The body turning to dust in Sanss hands. 

Sans huffs glaring at the dust left on the couch. "Good riddance." He speaks softly to himself. He turns and heads away. He needs to plan his next attack. He pauses though. He needs the murders to be linked. He needs to make an unsolved case. He turns and realizes what he could do. He uses a marker he finds, he'll take it with him, and writes a message on the wall. He makes sure to do his best to not write it like how he usually writes things. He makes it a bit more messy. Yet making sure it's still readable. 

You don't know how you betrayed me. 

Sans uses one last glance to the dust then teleports away. He needs to clean up and he puts the marker in his inventory. He can't be found out about. If he's spotted with dust on him then it could all be ruined, when they find out the dust on him isn't his own. He throws his clothes in the washing machine turning it on. He then teleports to the bathroom having a quick shower. He steps out when done drying himself off. He has more work to do. He just needs to get into clean clothes.

Papyrus shouldn't be back for a bit longer.

Sans wonders if he can get one more kill in before Papyrus comes back. He doesn't want Papyrus to go to Grillbys and not find him there. He has to be very careful with every step he takes in this. He goes to his room and puts on the same outfit he had on. He doesn't usually change his style all that much anyways. He is about to teleport away when he hears the front door open.

"Sans? Are you here? I'm home!"

Sans heads out of his room going over to greet his brother. "Hey Paps. I'm home. You have fun out there? I bet it went well since you're the Great Papyrus."

"Hello Sans." Papyrus picks him up and hugs him in which Sans hugs back. "Today went really well. As I am the Great Papyrus! Nyeh heh heh heh! Also Sans I picked up some spaghetti. We can make some delicious spaghetti!"

"Sounds fun bro." Sans agrees smiling softly at his brother. "You always make the best spaghetti out there. No one can compete. You even add a little magic to make others feel better. It's a very special Papyrus thing to make." 

"Of course not. I make the spaghetti very special after all! Nyeh heh heh heh!" Papyrus puffs his chest out proudly. 

"You sure do." Sans agrees and he settles down as Papyrus heads to go make it. He is rather relieved that the other has no idea about what he's doing. He'll have to continue tomorrow and take out as many as he can. He can't let Alphys share the same dreaded fate. He can stop it this time. He can do so by having his revenge. His hands clench tightly into fists since Papyrus won't see as he's not in the room. 

The next day.......

Papyrus is about to head for work and Sans gets on his sweater.

Sans looks to his brother who is making sure his boots are on right. "Have fun at work today Paps." 

Papyrus turns with his boots on all set to go. He smiles widely at his brother giving a wave to him. "I will! I'll see you when we both get get home!" He turns away with that and heads off on his way.

Sans lets out a small breath and teleports himself away. He ends up where the monsters had gathered before. He is hiding in the same spot. He hears someone enter the room. 

"Yes. Hello?" The footsteps are a bit all over the place, though there's no way Sans could mistake that voice. "I was calling about that project we've been discussing." He pauses to listen as Sans peeks out.

Sans can get a good look at this monster. 

This one is a deer monster and with some small horns. The deer monster boots on and hands with hooves as fingers. He stands tall with a business suit on that is dark blue in colour, and a red tie. His black eyes aren't paying enough attention to easily spot Sans. "I think we should talk to Alphys tomorrow or the day after about it." He informs whoever is on the other side of the line. "Yes sir. Don't worry. We'll make sure she can help us."

Sans clenches his teeth as he glares at the monster before ducking back into hiding. He has to stop this. He realizes what he must do. He has to kill all of the remaining ones today if possible. He'll have a bit of teleporting to do.

"Right. We can gather at your place later. I remember where it is. Don't worry I'll find my way there. Besides I'm at the office. If I did forget I would have looked it up in your file... Oh right. Back on track. I'll see you later." 

Sans summons a bone into one of his hands ready to strike. He can't let this meeting take place normally. He'd be against three monsters. He'll just take this one out then find that file. He'll have to crash that meeting with a visit from a past they don't remember. He peeks out again knowing he might have to be quick to strike. His target could already be about to leave the room. He sees his target grab something off of the desk in the room. He moves out of his hiding spot quickly hurrying towards the target. He is using blue magic on himself avoid noise. He slams the attack down onto the throat. He has to try to keep the victim from screaming out. He needs as much time as possible. He uses his other arm to do his best to try to restrain the monster. His arm wrapped around said monster. 

The deer monster falls backwards in shock and pain. His blood pouring out from the wound. 

Sans knows that if the thud is heard it'll draw attention. He manages to hold on and lowers them to the floor with as little noise as possible. He uses his blue magic to help with that. He keeps holding onto the deer from behind. He pulls the bone attack out stabbing the monster in the neck again. 

The deer monster struggles though his struggles are weakening. He turns and manages to get one eye to land on Sans. He tries to ask why though it only causes more blood to come out. 

Sans looks at the eye that spotted him with the darkest look he's ever given anyone. "You don't know how you've betrayed my family." He states then grabs the monsters head with both hands. He feels a burst of strength, possibly the adrenaline, and twists hard enough for the neck to snap. He feels a chill of satisfaction when he hears it snap. He stabs a bone through the monsters chest for good measure.

The monsters body fades away to dust almost immediately after. 

Sans gets up letting his attacks vanish. He heads over to the desk with a calm pace. He opens the first of seven drawers on the desk. He opens the bottom drawer looking at the contents within it. He sees that in this drawer there is some binders. He picks one up looking at it seeing that it is finances. He puts it back and tries the next drawer. He finds a bunch of office supplies in this one. He keeps trying the drawers finding project ideas, papers on finished projects, some tablets that need passcodes to unlock them, and finally some files that look promising. He pulls them out and finds that they are indeed files on the group. He opens one finding notes about how well they work and their achievements and failures. He finds the two addresses he'll need to try stop them. "It has to be today." He promises quietly to himself. "This can't wait another day." He puts the stuff back the way he found them. He teleports, to the place he is sure that they are gathering at, landing in front of a blind girl he didn't expect to be there.

The blind girl trips over him and he manages to not fall as well as catching her. "Ah. I'm so sorry. I didn't know you were there."

Sans doesn't dare speak as he helps her up then moves away to head to the house. He can't leave his voice for her to hear when he's about to kill. He peeks around the corner to see her trying to see if he is still there. He leaves her be knowing that she'll move on. He peeks inside the window spotting one monster he is targeting in the kitchen. He can see a lot of papers on the table, including a possible blueprint idea hanging partially over one edge. He teleports inside seeing an open doorway. He ducks behind the door to listen for now. He is going to get the last two he has to take down. 

"They should be here soon. This is a project I've been wanting to do for awhile. I am so excited that I was able to move past how I was feeling. I still don't understand why I felt like this was a bad idea. I know that this is a great idea!" The monster is a bunny monster with big floppy ears. He has a black nose with a diagonal scar across it, the top of the scar on his right sides going down to the left side of his lip, his fur is white though he has tan brown ears, he is wearing a black suit for this meeting, he even has a red tie, black socks since he is inside his home, and his eyes are a deep red color. "I'm not going to be a scared little rabbit. I'll show those who said all rabbit monsters are scared timid creatures! I won't let a bad feeling get in my way!"

Sans clenches his teeth. He knows that they don't remember though he supposes it's possible they get a feeling anyways. He could see some part still thinking that something bad happened, yet they don't understand why because they don't remember the past. He stays quiet to not be caught. He soon hears the footsteps of someone else entering the room. He keeps listening hoping to know if it's the other one he needs to kill. 

"Ah. Good to see you." The rabbit monster greets the other in a friendly manner. "I'm so glad you made it here safely."

"Yeah. I brought some extra papers like you asked." The other monster informs the bunny monster confirming to Sans who it is.

Sans peers around from where he is hiding to take a look. He spots that an alligator monster has now joined the bunny. He smiles widely to himself as this is perfect. He has everyone he needs to kill right here. He summons a bone in his hand. He can do it right now. 

The alligator monster has a dark green color, dark brown eyes, standing on two alligator feet, has two hands, and his tail poking out of the top of his pants. His clothes consist of a black laser that is undone, a blue button up shirt with the collar folded neatly though the top two buttons undone, black pants, and no socks or shoes. "Man shoes are so stuffy." He sighs as he sets the papers down with the others. "I gotta tell ya. I have no idea how you can walk with them on."

"I guess different ways we've been brought up." The bunny monster flashes a smile. 

Sans doesn't care about their names as he's already forgotten them. He's too focused on taking revenge for Gaster. He can finally end this. He can finally finish this then live his life satisfied that he did it. 

The alligator monster swishes his tail then lets out a low growl. "We're not alone."

Sans realizes he's been spotted. He has already lost track of making unsolved murders. He just needs to finish this. He leaps out slamming the bone attack he's holding, along with others that fly to attack, into the alligators back. He makes sure it punctures as many places as he can.

The alligator falls forward hitting the table hard enough to knock it over.

The papers are sent flying everywhere. They land on the floor even soaking up blood from the alligator monster.

Sans looks up from where he is on top of the alligator to look at the bunny. 

The bunny has pulled out what looks to be a blade with a carrot handle. "Sans?! What in the world is the meaning of this!?" 

Sans stands up letting go of the bones. His eyes give a dark look with anger and hatred at the bunny monster. He steps forward slamming a foot on the alligators head as hard as he can. He even puts some magic into it so it is strong enough to cause damage to the skull.

The bunny stands his ground still aiming the blade at Sans. "I demand that you answer me!" 

"You're the last one." Sans growls with his rage boiling as he glares right at the other. "I won't let you ruin another life!" He feels the alligators body start to fade to dust so he jumps up landing on a summoned Gaster blaster. He is crouched on one knee with a hand on the blaster. "You made this mistake once. I won't let you do it again with Alphys."

"What the hell are you going on about!?" The bunny summons another blade in his other hand as he prepares for battle. "This is the first time we've done it!"

"That's where you're wrong. Your memories are gone but your soul still tried to warn you." Sans stands up still on the blaster that's floating over the dust of the alligator. His hands at his sides. "I suppose I can humor you for a brief moment. You'll be dead either way." He adds as he continues to glare at the other monster. "You did this project with my father. You refused to listen. You sent him to a place that made everyone forget about him!" He closes his eye sockets. "Everyone but me." He opens his eyes again noticing the other is about to jump to attack. He can see the slight tremor go through the other. He hopes the part of the soul that tried to warn him is making him feel guilty. "No one will know who did it either. I killed everyone in your group." He adds to make sure that he shows he's serious about revenge. "And now." He raises his hand to chest level only to snap his fingers. 

A bone shoots up from under the bunny monster impaling him on the bone. 

The bunny monster struggles and drops his attacks to the ground.

"I am getting revenge for the father you tore away from me and my brother!" Sans jumps back landing on the ground behind the blaster. He charges it and fires it. He hears a gasp behind himself just before it fires though. He watches as the bunny monster is hit until he dusts. He lets the attacks vanish and sees a burned wall that had been hit by the blast for a moment. He's sure it could crumble if hit. "I did it." He starts to feel his soul feel lighter than ever before.

"BROTHER!!!" A scream happens behind him so Sans turns around.

Sanss dark look returning. He spots a female bunny monster who looks younger and is all white.

She's wearing a red plaid skirt, a purple shirt, and her ears are tied behind her head in a light purple bow. She turns her horrified look to glare at Sans. "You killed him!" She rushes forward managing to dodge some bones. She doesn't stop even as she is hit in the shoulder. 

Sans gets ready to teleport and summon more attacks.

The girl manages to slice his chest causing his attacks to disappear. She just finished her slash when he teleports away so she's not taken with him. She is breathing heavily before dropping her blade. She falls to her knees then to the floor sobbing and screaming in grief. 

Sans lands in a part of town he didn't mean to go to. His magic screwed up as he was hit. He lands on the ground leaving blood. He coughs up some more blood and glances around. He doesn't see anyone outside. He swears it's possibly apartments or office buildings. His gaze starts to get blurry and he drags himself into the alley hoping that someone will be in their backyard. He doesn't even notice the blood he is leaving behind. He stops to look up at a tall brick wall. His arms wobble and he collapses completely to the ground again. His eyes closing as the world feels like it's spinning. "Sorry Paps." He whispers softly as his body turns to dust.

Papyrus and Undyne are enjoying the day and going for a walk together. They are talking happily as Undyne shares some time she spent with Alphys enjoying the day. 

Papyrus pauses as they turn the corner.

Undyne stops laughing as soon as she sees his worried look. She turns to see what he's looking at and gasps upon seeing the blood. "Someone's hurt!"

The two of them hurry over and follow the blood into the alley only to both freeze.

"SANS!!!!" Papyrus screams hurrying over to the dust with Sanss signature sweater. He falls to his knees next to the dust grabbing the sweater. His eyes filling with tears like a waterfall. He falls forward to be hunched over crying loudly as he clutches his brothers jacket.

Undyne clenches her hands into fists letting some tears fall for her fallen friend. She can't believe something like this happened. She can't think of anyone who hated Sans. She doesn't understand why this had to happen. She moves forward and sits next to her friend. She brings him into a hug trying to comfort him as he cries.


End file.
